This invention relates generally to an improvement in an electrostatic reproduction machine, but more particularly to an improved corona generating device for such a machine.
In the practice of xerography as described in U.S. Pat. No. 2,297,691 to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material affixed to a conductive backing is used to support electrostatic images. In the usual method of carrying out the process, the xerographic plate is electrostatically charged uniformly over its surface, and then exposed to a light pattern of the image being reproduced to thereby discharge the charge in the areas where light strikes the layer. The undischarged areas of the layer thus form an electrostatic charge pattern or electrostatic latent image in conformity with the configuration of the original pattern.
The latent electrostatic image is developed by contacting it with a finely divided electrostatically attractable material, such as a resinous powder. The powder is held in the image areas by the electrostatic fields on the layer. Where the field is greatest, the greatest amount of material is deposited, and where the field is least, little or no material is deposited. Thus, a powder image is produced in conformity with the image of the original being produced. The powder image is subsequently transferred to a sheet of paper or other transfer member, and suitably affixed thereto to form a permanent copy.
The latest concept for electrostatic reproduction machines utilizes high speed flash exposure of the document, and a moving photoconductive material in the form of an endless belt which is continuously charged. Additionally, such reproduction machines are provided with a developing system which supplies toner particles in relatively large quantities for solid area coverage, such as a magnetic brush developing apparatus. Thus, after the belt passes the magnetic brush assembly, for example, a xerographic powder image is formed on the belt which corresponds to the electrostatic latent image. This powder image is then transferred to a support surface (e.g., a sheet of paper) to which it is fused by a fusing assembly whereby the powder image is caused to adhere to the support surface permanently.
The latest electrostatic reproduction machines are high speed machines which print copies at a rate substantially in excess of any previous electrostatic reproduction machine, and are intended to compete with other types of printing machines, e.g., offset printing machines. Because of this, it is desired that the quality of the copies made, be extremely high. Important to high quality copies are effective corona generating devices. Numerous corona generating devices are used in such high speed machines. For example, a corona generating device is used to initially place a charge on the photoreceptor prior to exposure. Corona generating devices are also used prior to the transfer operation to place an appropriate charge on the background so as to prevent or minimize the transfer of background particles. In some machines, corona generating devices are also used to effect the transfer operation. After the transfer operation, corona generating devices are also used to detack the transfer member from the photoreceptor, and to place an appropriate charge on the photoreceptor so as to loosen any residual toner on the photoreceptor so that it may be more easily removed with a brush cleaning apparatus. Thus, as can be seen, corona generating devices are very important to the proper operation of such machines. Many corona generating devices have or must have conductive shields; to keep such corona generating devices operating most effectively, it is highly important that toner be efficiently removed at periodic intervals, because toner accumulations on either the shield or corona wire affect the operation of the devices. The efficiency of a corona generating device decreases substantially as the density of dust accumulation on the device increases. As a result there is a sharp decrease in the quality of the copies made.
Thus, to ensure high efficiency, the corona generating device requires frequent cleaning and maintenance. For example, in order to maintain the entire machine operating effectively it has been necessary to clean corona generating devices completely after several hundred reproductions, and even sooner with machines operating at very high rates. In many instances, this requires removing corona generating devices from a machine, and cleaning the entire assemblies including wires, and shields with a suitable cleaning solution. Needless to say, this is a time consuming operation, and requires that the machine be out of operation for a considerable period of time.
On many reproduction machines manufactured today, however, the corona generating devices have built-in mechanisms for cleaning the wires, or both the wires and shields. The prior art discloses various arrangements for doing this. U.S. Pat. Nos. 2,614,901 and 3,496,362 and IBM Technical Disclosure Bulletin (Vol. 11, No. 8, p. 1025, January, 1969) all show various arrangements for cleaning corona wires only. Offenlegungsschrift 2,302,212 shows an arrangement for manually cleaning both the wire and shield of a corona generating device. U.S. patent applications, Ser. Nos. 367,607 and 400,077, assigned to Xerox Corporation, discloses additional arrangements for cleaning both the wire and shield of a corona generating device, the former being intended for manual operation, and the latter for automatic operation. For the high speed reproduction machines presently being manufactured, corona generating devices must be provided with built-in cleaning mechanisms for cleaning the wires and shields in order to utilize the machines most efficiently and produce good quality copies. Preferably, such cleaning mechanisms should be electrically operated (e.g., by a motor) instead of manually operated. Because such high speed machines are highly complex mechanisms having thousands of parts, Xerox, the assignee of the instant application, makes every effort to reduce costs wherever possible, and to efficiently utilize whatever space is available in the machines. Thus, what is needed is a corona generating device having an improved built-in cleaning mechanism, which mechanism can be motor or automatically driven, occupies a minimum amount of space, has a minimum number of parts, is relatively economical to manufacture, and permits one to readily remove the device from the machine for routine maintenance.